Cubital Tunnel

The cubital tunnel is located posterior to the medial epicondyle and contains the ulnar nerve and posterior recurrent ulnar vessels surrounded by fat.

• The medial margins of the trochlea and olecranon form its floor, which is lined by the posterior band of the ulnar collateral ligament. A hypoplastic trochlea can predispose patients to ulnar nerve dislocation. The ulnar collateral ligament relaxes and bulges medially during elbow flexion, which results in narrowing of the cubital tunnel.
• The arcuate ligament forms its roof. This is a fibrous band between the ulnar and humeral heads of the flexor carpi ulnaris muscle and is also known as Osborne's band and the cubital tunnel retinaculum. The arcuate ligament becomes taut with flexion of the elbow. Congenital absence, laxity or a tear of the arcuate ligament can lead to ulnar nerve dislocation.
• The medial epicondyle makes up its anterior border.

The normal cubital tunnel should contain fat signal surrounding the intermediate-signal–intensity ulnar nerve. Posterior recurrent ulnar vessels can be seen as dot-like, T1-hypointense structures adjacent to the ulnar nerve

The cubital tunnel is the most common site of ulnar nerve compression at the elbow. Cubital tunnel syndrome is due to narrowing of the cubital tunnel or repetitive stress on the ulnar nerve. Elbow flexion in normal subjects results in narrowing of the tunnel by stretching the arcuate ligament; bulging of the medial head of the triceps muscle, which pushes the ulnar nerve anteromedially; and relaxing the ulnar collateral ligament, which bulges medially.

Images through the cubital tunnel during elbow flexion can reveal findings pertinent to cubital tunnel syndrome, including narrowing of the cubital tunnel, attenuation of the perineural fat, bulging of the medial head of the triceps (located more superiorly than the presented slice), and flattening of the ulnar nerve.

Masses in or around the cubital tunnel can cause ulnar nerve compression, including bursae, ganglia, inflammatory synovitis, osteoarthritis, ectopic calcifications, anomalous muscles (e.g., anconeus epitrochlearis) or ligaments (e.g., ligament of Struthers, normally associated with median nerve compression).

Fluid-sensitive sequences often reveal increased signal intensity of the ulnar nerve in the setting of cubital tunnel syndrome.

References

Chapters 2, 10, 11, and 13. In Chung CB and Steinbach LS. MRI of the Upper Extremity: Shoulder, Elbow, Wrist, and Hand. Lippincott Williams & Wilkins. 2010.